How a Percussion Driven Earth Anchor Works
There are three steps to the installation of an anchor system:
Driving the Anchor
Removing the Rods
The same three basic steps apply to the installation of all anchor systems, from the smallest S2 to the
largest B10 .
Typical Anchor Behaviour
Loadlock – The first stage is where a load is applied to rotate the ground anchor into its loadlocked position. Elements of both load and extension are present.
Compaction & Load – The second stage is where the anchor system is generating a frustum of soil immediately in front of the ground anchor. At this point load normally increases with minimum extension. The soil type will affect the overall extension.
Maximum Load Range – The third stage is where the ground anchor produces its ultimate load. As the anchor load approaches the bearing capacity of the soil, the rate of increase in load will reduce until bearing capacity failure of the soil takes place.
Bearing Capacity Failure – Caution: If the mechanical shear strength of the soil is exceeded, the residual load will decrease with continued extension as the earth anchor shears through the ground.
Stress Distribution and Bearing Capacity
The stress distribution in front of a loaded ground anchor can be modelled using foundation theory. The ultimate performance of an anchor within the soil is defined by the load at which the stress concentration immediately in front of the anchor exceeds the bearing capacity of the soil.
Factors that will affect the ultimate performance of the anchor include:-
- Physical properties of the soil
- Size of the anchor
- Depth of installation
- The load applied
Platipus anchors perform exceptionally well in a granular soil, displaying short loadlock and extension characteristics, a broad frustum of soil immediately in front of the earth anchor and extremely high loads.
Stiff cohesive soils, such as boulder clays, can also give outstanding results. However, weaker cohesive soils, like soft alluvial clays, can result in long loadlock and extension distances and a small frustum of soil in front of the ground anchor. Consequently these conditions require a larger size of anchor and if possible a deeper driven depth to achieve design loads.
Granular Soils (Drained)
Cohesive Soils (Undrained)